This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-212486 filed on Jul. 12, 2001.
The present invention relates to a charging condition detecting apparatus for detecting the charging condition of a large number of unit cells which are connected in series to form a set battery.
Various electric vehicles (EV) and hybrid electric vehicles (HEV) are proposed, because these vehicles generate no or less exhaust gas. As a secondary battery used as the power source of these HEV and EV, a lead-acid battery, nickel-cadmium battery, nickel-hydrogen battery or the like are known. Moreover, in recent years, attention is paid to a lithium battery because this battery has a higher weight energy density, about four times the lead-acid battery of the same capacity and about two times the nickel-hydrogen battery. These battery can therefore be expected to provide reduction in size and weight.
The Japanese Unexamined Utility Model Publication H2-136445 discloses a method in which a cell voltage of each unit cell is detected by using voltage detectors which are connected in parallel to each unit cell. In this method, the charging/discharging current is controlled so that the cell voltage of any unit cell does not exceed, at the time of charging operation, the preset upper limit voltage and does not become lower than the preset lower limit voltage at the time of discharging operation.
Here, FIG. 8A is a circuit diagram showing an example of a charging condition detecting apparatus P-CMUi which divides a set battery into cell groups CGi (i=1 to m), each of which is constructed by n unit cells, and detects whether there is a unit cell in the over-charge or over-discharge condition among those Ci1 to Cin forming the cell group CGi.
The charging condition detecting apparatus P-CMUi has an over-charge determining circuit Puij which determines, for every unit cell Ci1 to Cin forming the cell group CGi, whether the unit cell Cij (j=1 to n) is in the over-charge condition or not and generates a cell over-charge detection signal CUij indicating the result of determination. It also has an over-discharge determining circuit PLij which determines whether the unit cell Cij is in the over-discharge condition or not and generates a cell over-discharge detection signal CLij indicating the result of determination.
As shown in FIG. 8B, each over-charge determining circuit PUij is constructed by a voltage dividing circuit 120 comprising resistors RUa and RUb to divide a cell voltage VCij across the unit cell Cij, a constant voltage circuit 122 comprising a resistor RUc and a voltage generation source DU to generate a constant upper limit reference voltage VRU and a comparator 123. To the comparator 123, a voltage depending on the cell voltage VCij is impressed to its non-inverting input via the voltage dividing circuit 120 and the upper limit reference voltage VRU generated by the constant voltage circuit 122 is impressed to its inverting input.
Moreover, each over-discharge determining circuit PLij is constructed by a voltage dividing circuit 124 comprising resistors RLa, RLb to divide the cell voltage VCij, a constant voltage circuit 126 comprising a resistor RLc and a voltage generation source DL to generate a constant lower limit reference voltage VRL and a comparator 127. To the comparator 127, a voltage depending on the cell voltage VCij is impressed to its non-inverting input via the voltage dividing circuit 124 and the lower limit reference voltage VRL generated by a constant voltage circuit 126 is impressed to its inverting input.
However, the voltage generation sources DU, DL generate the reference voltages VRU, VRL by utilizing, for example, a forward voltage of a diode and a breakdown voltage of a Zener diode. The upper limit reference voltage VRU generated by the voltage generation source DU of the over-charge determining circuit PUij is set to a value, VUxc2x7Rub/(RUa+RUb), obtained by dividing the upper limit value VU of the allowable voltage range of the cell voltage VCij in a voltage dividing ratio of the voltage dividing circuit 120. The lower limit reference voltage VRL generated by the voltage generation source DL of the over-discharge determining circuit PLij is set to a value, VLxc2x7RLb/(RLa+RLb), obtained by dividing the lower limit value VL of the allowable voltage range of the cell voltage VCij in a voltage dividing ratio of the voltage dividing circuit 124 comprised of resistors RLa, RLb.
The over-charge detection signal CUij generated by the over-charge determining circuit PUij becomes high level indicating that the unit cell Cij is in the cell over-charge condition when the cell voltage VCij is larger than the upper limit value VU of the allowable voltage range. It becomes low level when the cell voltage is smaller than the upper limit value VU. Moreover, the cell over-discharge detection signal CLij generated by the over-discharge determining circuit PLij becomes low level indicating that the unit cell Cij is in the over-discharge condition when the cell voltage VCij is smaller than the lower limit value VL of the allowable voltage range.
In addition, as shown in FIG. 8A, the charging condition detecting apparatus P-CMUi is provided with a logical sum (OR) circuit 132 which provides a high level output when any one of the cell over-charge detection signals CUi1 to CUin from each over-charge determining circuit PUi1 to PUin is in the high level. The detecting apparatus P-CMUi is further provided with a logical product (AND) circuit 133 which provides a low level output when any one of the cell over-discharge detection signals CLi1 to CLin from each over-discharge determining circuit PLi1 to PLin is in the low level. Thereby, an output of the OR circuit 132 is used as a groop over-charge detection signal OUi, while an output of the AND circuit 133 as a group over-discharge detection signal OLi.
That is, when all unit cells Ci1 to Cin forming a cell group CGi are in the normal charging condition (VLxe2x89xa6VCijxe2x89xa6VU), the group over-charge detection signal OUij becomes low level, while the group over-discharge detection signal OLij becomes high level. On the other hand, when any one of the unit cells Ci1 to Cin is in the over-charge condition (VCij greater than VU), the group over-charge detection signal OUi becomes high level. When any one of the unit cells is in the over-discharge condition (VCij less than VL), the group over-discharge detection signal OLi becomes low level.
However, the charging condition detecting apparatus P-CMUi still has a problem that the unit cell Cij is continuously used under the over-charge or over-discharge condition. Thus the unit cell Cij, more specifically a set battery as a whole, can no longer be used because this apparatus cannot detect the over-charge condition or over-discharge condition of the unit cell Cij when the cell overcharge detection signal CUij, cell over-discharge detection signal CLij, group over-charge detection signal OUi or group over-discharge detection signal OLi is fixed to the signal level indicating the normal condition for some reason.
It is therefore an object of the present invention to detect faults or irregular conditions of a charging condition detecting apparatus for detecting, in the simplified structure, the charging condition of unit cells in every group.
According to the first aspect of the present invention, a charging condition detecting apparatus is respectively provided with a first voltage comparator and a second voltage comparator for each unit cell forming a chargeable/dischargeable set battery. In the first voltage comparator, when a cell voltage which is a voltage across the unit cell is higher than a first threshold value voltage which is set to the upper limit value of the allowable voltage range of the cell voltage, an output of this first comparator becomes an active level, while in the second voltage comparator, when the cell voltage of unit cell is lower than a second threshold value voltage which is set to the lower limit value of the allowable voltage range of the cell voltage, an output of this second comparator becomes an active level.
A first logical sum calculation circuit generates an over-charge detection signal by obtaining a logical sum of the outputs of the first voltage comparator provided for each unit cell. A second logical sum calculation circuit generates an over-discharge detection signal by obtaining a logical sum of the outputs of the second voltage comparator provided for each unit cell.
That is, if any one of the unit cells forming a set battery enters the over-charge condition (exceeding the upper limit value), the over-charge detection signal becomes the active level. If any one of the unit cells forming a set battery enters the over-discharge condition (lowering the lower limit value), the over-discharge detection signal becomes the active level.
Particularly, a threshold value voltage changing circuit changes, depending on an external command, a first threshold value voltage to a first inspection value which is lower than the lower limit value of the allowable voltage range. It also changes a second threshold value voltage to a second inspection value which is higher than the upper limit value of the allowable voltage range. Meanwhile, a first logical product calculation circuit generates a first fault detection signal by obtaining a logical product of
the outputs of the first voltage comparator provided for every unit cell, while a second logical product calculation circuit generates a second fault detection signal by obtaining a logical product of the outputs of the second voltage comparator provided for every unit cell.
According to the charging condition detecting apparatus of the present invention, not only it can be detected whether there are unit cells in the over-charge and over-discharge conditions or not among those forming a set battery based on the over-charge detection signal and over-discharge detection signal, but also a fault of a first voltage detecting circuit for generating the over-charge detection signal and the first logical sum calculation circuit and a second voltage detecting circuit for generating the over-discharge detection signal and the second logical sum calculation circuit can be detected by monitoring the first and second fault detection signals after the change of the first and second threshold value voltages with the threshold value voltage changing circuit.
That is, the outputs of the first and second voltage comparators after the change of the first and second threshold value voltages are in the active level and therefore outputs of a first and a second fault detection circuits have also to be in the active level. Accordingly, when an output of the first or the second fault detection circuit is not in the active level, it can be determined that a fault exists in any output of the first or second voltage comparator.
The active level may be set to any one of the high level and low level. When the active level is set as the high level, the first and second logical sum calculation circuit may be formed as a logical sum (OR) circuit and the first and second logical product calculation circuits may be formed as a logical product (AND) circuit. When the active level is set, on the contrary, as the low level, the first and second logical sum calculation circuits may be formed as a logical product (AND) circuit and the first and second logical product calculation circuits may be formed as a logical sum (OR) circuit.
According to the second aspect of the present invention, in a charging condition detecting apparatus, the voltage comparator provided for every unit cell forming a chargeable/dischargeable set battery provides an output in the active level when the cell voltage which is a voltage across the unit cell exceeds the threshold value voltage which is set to a boundary value of the allowable voltage range of the cell voltage in the outside of this voltage range and the logical sum calculation circuit generates a charging condition detection signal by obtaining a logical sum of the outputs of the voltage comparator provided for every unit cell.
That is, an output of the voltage comparator is in the active level, under the condition that the upper limit value of the allowable voltage range is set as the boundary value, when the cell voltage exceeds this upper limit value. When the lower limit value of the allowable voltage range is set as the boundary value, the output of the voltage comparator is in the active level when the cell voltage is lower than the lower limit value.
The threshold value voltage changing circuit changes, depending on an external command, a threshold value to an inspection value for setting an output of the voltage comparator to the active level from the boundary value when the cell voltage of unit cell is within the allowable voltage range and the logical product calculation circuit generates a fault detection signal by obtaining a logical product of the outputs of the voltage comparator provided for every unit cell.
More practically, when the upper limit value of the allowable voltage range is set as the boundary value, the inspection value is set to a value lower than the lower limit value of the allowable voltage range. When the lower limit value of the allowable voltage range is set as the boundary value, the inspection value may be set to a value larger than the upper limit value of the allowable voltage range.